Apparatus for an aircraft proximity warning system

ABSTRACT

The azimuth quadrant of an intruder aircraft is determined with a triangulation technique which makes use of the arrival times of cooperative signals from the intruder aircraft. The signals from the intruder are received by three antennas and depending on the antenna arrival times, logic signals are generated which set a pair of flip-flops to one of four states (1,1), (0,1), (0,0) or (1,0) indicating that the intruder is in the front, right, rear, or left quadrant, respectively.

United States Patent [191 Bennett et al.

[ 51 Sept. 25, 1973 APPARATUS FOR AN AIRCRAFT PROXIMITY WARNING SYSTEMInventors: David B. Bennett, Minneapolis;

Charles P. Harman, Roseville; Robert J. Follen, Minneapolis, all ofMinn.

Assignee: Honeywell Inc., Minneapolis, Minn.

Filed: June 23, 1971 Appl. No.: 155,747

U.S. Cl. 343/113 R, 343/112 CA, 343/16 R Int. Cl. G015 3/50 Field ofSearch 343/113 R, 112 CA,

References Cited UNITED STATES PATENTS 1/1970 Sherrill et a1. 343/113 R3,605,096 9/1971 Fothergill ct al 343/113 R Primary ExaminerBenjamin A.Borchelt Assistant ExaminerDenis H. McCabe Attorney-Charles J. Ungemachet a1.

[57] ABSTRACT The azimuth quadrant of an intruder aircraft is determinedwith a triangulation technique which makes use of the arrival times ofcooperative signals from themtruder aircraft. The signals from theintruder are received by three antennas and depending on the antennaarrival times, logic signals are generated which set a pair offlip-flopsto one of four states 1,1 (0,1 (0,0) or (1,0) indicating that theintruder is in the front, right, rear, or left quadrant, respectively.

2 Claims, 2 Drawing Figures REGION I110, 11

REGION W0, 0)

/\ REGION m (0,01

Patented Sept. 25, 1973 3,761,930

2 Sheets-Sheet 2 REGION ll (0, I)

REGION m (0. 0)

FIG. 2

INVENTORS DAVID 5. BE ETT ROBERT J. F LEN CHARLES R HARMAN ATTORNEYAPPARATUS FOR AN AIRCRAFT PROXIMITY WARNING SYSTEM BACKGROUND In someaircraft proximity warning systems the azimuth of the intruder aircraftcausing the warning is not provided. This invention is designed forinclusion in a proximity warning system to indicate the azimuth quadrantof the intruder aircraft.

SUMMARY Azimuth information is obtained by making use of a triangulationtechnique wherein a signal transmitted by one aircraft (the intruding orresponding aircraft) in response to a signal from a second aircraft (theinterrogating aircraft) is received at three spaced antennas on thesecond aircraft. The azimuth of the intruder is a function oftherelative arrival times of the signal at the three antennas. Theinvention provides circuitry for comparing the arrival times of thesignal and circuitry for developing logic signals depending upon theresult of the comparisons. The logic signals are used to set afour-state device, such as a flip-flop pair, to one of the four states,indicating the azimuth quadrant of the intruder.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of a circuitfor determining the azimuth quadrant of an intruder aircraft; and,

FIG. 2 illustrates a typical antenna installation on a helicopter andidentifies the azimuth quadrants and coordinates thereof.

DESCRIPTION OF TI-IE PREFERRED EMBODIMENT In the system of FIG. 1 theazimuth of an intruder is obtained by making use of the differences inthe arrival times of the intruders response signal at three differentantennas. An example of an antenna installation is shown in FIG. 2 wherethree antennas A, B and C, mounted on a helicopter, provide sufficientinformation to determine azimuth within one of the four 90 regions I,II, III or IV within a minimum of data processing. Region I is theforward quadrant. region 11 is the right quadrant, region 111 is therear quadrant and region IV is the left quadrant. Each quadrant ischaracterized by two coordinates (azimuth number 1, azimuth number 2) asfollows:

Region Coordinates I 1 ,1 11 (0,1 111 (0,0) IV 1 ,0)

For example, an intruder in region I would be characterized bycoordinates (1,1) and signals respresenting these coordinates aredeveloped by the system-of FIG. 1.

Using the dimensions shown in FIG. 2 of 12 feet between the two forwardantennas B and A and 33 feet between a line drawn between the forwardantennas and the rear antenna C, the azimuth regions can be defined interms of the intruder response signal arrival times t 1,, and t atantennas A, B and C, respectively. A response signal from an intruder inregion I arrives at either antenna A or B at least 28 nanoseconds beforeit arrives at antenna C. The closest an intruder can be to antenna C andstill be in Region I is to be on one of the two boundaries. Assume, forexample, that the intruder is on the boundary represented by the dashedline passing through antenna B and that the intruder is out a long wayon the boundary, compared to the dimensions between antennas A, B, andC. The difference in the arrival times at antennas B and C isproportional to the difference in the distance between antennas B and C.This is approximately equal to (6 2 27 sin 45) ft 27.55 ft. This resultis obtained by projecting the line from the intruder to antenna C ontothe dashed line passing through antenna B. Since electomagnetic energytravels about 984 feet per microsecond, 27.55 feet divided by 984 feetper second equals about 28 NS. A response signal from an intruder inregion II arrives at antenna A before it arrives at antenna B andarrives at antenna A less than 28 nanoseconds before it arrives atantenna C or arrives at antenna C equal to or less than 19.4 nanosecondsbefore it arrives at antenna A. The 19.4 NS difference in arrival timeis reached by assuming an intruder is on the right boundary of RegionIII and out a long way compared to the dimensions between the antennaarray. This is the closest an intruder can be to antenna A and still bein Region Ill. The difference in arrival time is proportional to thedifference in distance which is approximately 27 sin 45 ft which is thelength of the line from the center of the helicopter to antenna Cprojected onto the dashed line running through antenna B. This is about19.09 feet which when divided by 984 feet per second results in adifference in arrival time of 19.4 NS. A response signal from anintruder in region 111 arrives at antenna C at least 19.4 nanosecondsbefore it arrives at antenna A or B. The relationship in region IV isanalogous to that in region 11. A response signal from an intruder inregion IV arrives at antenna B before it arrives at antenna A andarrives at antenna B less than 28 nanoseconds before it arrives atantenna C or arrives at antenna C equal to or less than 19.4 nanosecondsbefore it arrives at antenna B.

The time relationships in the various regions are expressed moreformerly as follows:

Region I 2 1 -1,, 2 28NS or 2 -h, z 28NS Region II r,, t,, and 19.4NS 2-1, 28NS Region IV t t and 19.4NS z t,,t 28NS Referring to FIG. 1, anintruder in region I is determined in thefollowing way. The signals fromantenna A and B are applied to an OR gate 10, the output of which isapplied to a delay line 12 having a delay of approximately 28nanoseconds. The delayed signal from line 12 and the signal from antennaC are applied to a comparator 14 which develops a positive output signal(which will be called a logical l or 1) if the delayed signal isreceived first and a negative signal (which will be called a logical 0or 0) if the delayed signal is received last. The output signals fromcomparator 14 are applied to a pair of OR gates 16 and 18 which whenactivated set flip-flops 20 and 22, respectively. The logical states offlip-flops 20 and 22 correspond to the coordinate azimuth number I andazimuth number 2, respectively. Therefore, when a response signal isreceived from an intruder in region 1 comparator 14 develops a logical 1output signal, both OR gates 16 and 18 are activated, and bothflip-flops 20 and 22 are set to the logical 1 state. With bothflip-flops 20 and 22 set to a logical 1 state the coordinates are (1,1)and the azimuth of the intruder is indicated as region 1. Flip-flops 20and 22 are periodically reset.

An intruder in region II is determined in the following way. The signalfrom antenna C is applied to a delay line 24 having a delay ofapproximately 19.4 nanoseconds. The delayed signal and the output signalof OR gate are applied to a comparator 26 which develops a positiveoutput signal 1) if the delayed signal is received last and a negativeoutput signal (0) if the delayed signal is received first. The outputsignal developed by comparator 14 is also applied to comparator 26 suchthat comparator 26 is inhibited if the output of comparator 14 is in a 1state. (Some signals from intruders in region I which normally causecomparator 14 to respond would also cause comparator 26 to respond if itwas not inhibited.) The signals from antennas A and B are also appliedto a comparator 32 which develops a negative output signal (0) if thesignal from antenna A arrives before that from antenna B and develops apositive output signal (1) if the signal from antenna B arrives beforethat from antenna A. The output of comparator 26 is applied to a pair ofAND gates 28 and 30 and the output of comparator 32 is also applied toAND gate 28 and to an inverter 34. The output of inverter 34 is appliedto AND gate 30. The outputs of AND gates 28 and 30 are applied to ORgates 16 and 18 respectively.

When a response from an intruder in region II is received the followingsituation exists. The output of comparator 26 is 1", the output ofcomparator 32 is 0, the output of inverter 34 is l and AND circuit 30 isactivated. The activation of AND gate 30 causes OR gate 18 to beactivated and flip-flop 22 is set to the I state. Although AND gate 30is activated AND gate 28 is not activated, therefore the output of ANDgate 28 is 0 as is the output of comparator l4 and OR gate 16 is notactivated. Therefore flip-flop remains in the 0" state and thecoordinates (0,1) for region II are indicated.

When a response signal is received from an intruder in region IV thefollowing situation exists. The output of comparator 26 is 1" just at itwas for a region II situation but whereas the output of comparator 32was 0" for a region II situation it becomes 1 for a region IV situation.Therefore AND gate 28, rather than AND gate 30, is activated which inturn activates OR gate 16 and flip-flop 20 is set to the l." Since theoutput of comparator 14 in a region IV situation is 0 and since AND gateis deactivated OR gate 18 is also deactivated and flip-flop 22 remainsin the 0 state. Therefore flip-flops 20 and 22 indicate the coordinates(1,0), corresponding to an intruder in region IV.

When a response from an intruder in region III is received the followingsituation exists, the out-puts of both comparator 14 and comparator 26are in the 0" state. Therefore AND gate 28, AND gate 30, and OR gate 16are not activated and flip-flops 20 and 22 remain in the 0" state,indicating the coordinates (0,0) for an intruder in region III.Therefore region III aircraft are identified as aircraft which are notin regions I, II, or IV.

A specific embodiment has been described, but the invention is notlimited thereto. Other embodiments may occur to those skilled in the artand the invention is to be limited only by what is claimed.

We claim:

1. In a proximity warning system for an aircraft, apparatus fordetermining the azimuth of signals from an intruder aircraft comprising:

means including three antennas A, B and C, for receiving the signalsfrom the intruder aircraft, antennas A and B mounted in a first quadrantof the aircraft and antenna C in a second quadrant;

means for delaying the signals received by antennas A and B;

first comparator means responsive to the delayed signals from antennas Aand B and the undelayed signals received by antenna C for comparing thetiming of the delayed signals with that of the undelayed signals anddeveloping an output signal if the delayed signals occur first;

means for delaying signals received by antenna C;

second comparator means responsive to delayed signals received byantenna C and undelayed signals received by antennas A and B, forcomparing the timing of the delayed signals with that of the undelayedsignals and developing an output signal if the undelayed signals occurfirst, the second comparator means being inhibited, however, if thefirst comparator means has developed an output signal;

third comparator means responsive to undelayed sig nals received byantennas A and B and developing an output signal if the signal receivedby antenna A occurs first;

means responsive to the output signal of said third means for invertingsaid output signal;

a first AND circuit responsive to the output signals of the second andthird comparator means and developing an output signal;

a second AND circuit responsive to the output signal of the secondcomparator means and the inverted output signal of the third comparatormeans and developing an output signal;

a first OR circuit responsive to the output signals of the firstcomparator means and the first AND circuit and developing an outputsignal;

a second OR circuit responsive to the output signals of the firstcomparator means and the second AND circuit and developing an outputsignal;

a first flip-flop circuit, developing an output signal in response tothe output signal of the first OR circuit; and,

a second flip-flop circuit, developing an output signal in response tothe output signal of the second OR circuit, the combined states of thefirst and second flip-flops denoting the quadrant of the intruderaircraft.

2. The apparatus of claim 1 wherein the first and second quadrants ofthe aircraft are the forward and rear quadrants, respectively.

1. In a proximity warning system for an aircraft, apparatus fordetermining the azimuth of signals from an intruder aircraft comprising:means including three antennas A, B and C, for receiving the signalsfrom the intruder aircraft, antennas A and B mounted in a first quadrantof the aircraft and antenna C in a second quadrant; means for delayingthe signals received by Antennas A and B; first comparator meansresponsive to the delayed signals from antennas A and B and theundelayed signals received by antenna C for comparing the timing of thedelayed signals with that of the undelayed signals and developing anoutput signal if the delayed signals occur first; means for delayingsignals received by antenna C; second comparator means responsive todelayed signals received by antenna C and undelayed signals received byantennas A and B, for comparing the timing of the delayed signals withthat of the undelayed signals and developing an output signal if theundelayed signals occur first, the second comparator means beinginhibited, however, if the first comparator means has developed anoutput signal; third comparator means responsive to undelayed signalsreceived by antennas A and B and developing an output signal if thesignal received by antenna A occurs first; means responsive to theoutput signal of said third means for inverting said output signal; afirst AND circuit responsive to the output signals of the second andthird comparator means and developing an output signal; a second ANDcircuit responsive to the output signal of the second comparator meansand the inverted output signal of the third comparator means anddeveloping an output signal; a first OR circuit responsive to the outputsignals of the first comparator means and the first AND circuit anddeveloping an output signal; a second OR circuit responsive to theoutput signals of the first comparator means and the second AND circuitand developing an output signal; a first flip-flop circuit, developingan output signal in response to the output signal of the first ORcircuit; and, a second flip-flop circuit, developing an output signal inresponse to the output signal of the second OR circuit, the combinedstates of the first and second flip-flops denoting the quadrant of theintruder aircraft.
 2. The apparatus of claim 1 wherein the first andsecond quadrants of the aircraft are the forward and rear quadrants,respectively.